a) Field of the Invention
This invention relates to an automatically operated shovel, and especially to an automatically operated shovel improved in digging performance.
b) Description of the Related Art
Power shovels are known as a representative example of construction machinery for many years. In recent years, power shovels are designed to perform work by an automated operation when the work consists of repetitions of a series of simple work ranging from digging to hauling or dumping. To permit an automatic operation of a power shovel, however, there are a variety of problems which must be solved.
For example, an object under digging may be soft like soil, may comprise soft portions and hard portions mixed together like soil and rocks, or may comprise only hard portions like rocks cut off from a working face. To assure an efficient, stable operation of an automatically operated shovel under control irrespective of the conditions of the object under digging, certain measures are required.
To meet such requirements, a method is proposed in JP 7-259117 A. This method features generation of control command values in an automatic digging apparatus on the basis of values preset depending on various soil conditions, respectively. These various soil conditions correspond to objects under digging in the present invention. Described more specifically, this apparatus is provided with hydraulic cylinders for operating a boom, an arm and a bucket, respectively, and also with a lookup table having, for example, control characteristics such that the boom is not raised within a range where the pressure of a cylinder for the arm is low but a command value for a boom-raising speed is changed proportionally depending on the condition of soil when the pressure exceeds a predetermined value. It is disclosed that based on a detected arm pressure, a command value is outputted for the control of the boom cylinder in accordance with the corresponding control characteristics set in the lookup table. In this prior art, the lookup table has to be set by making reference to soil conditions from time to time or has to be set separately in a different manner.
The method of the above-described conventional art, therefore, requires advance setting of soil conditions. It is hence necessary to furnish information on the soil conditions by a certain method. For example, with respect to soil and rocks cut out from a working front at a quarry, it is necessary to determine by a suitable method whether the soil and rocks contain more soil or more rocks. No problem arises for this determination in the case of a digging apparatus which is attended by an operator and automatically performs only digging. In the case of a fully operatorless digging apparatus, a system is additionally required to determine conditions of soil, resulting in a more complex and costly digging apparatus. Even if such a system is employed, it is still difficult to determine the kind of an object under digging on a real-time basis when the object under digging is not homogeneous at all like stone-mixed soil.